function Ajax($method,$url,$parmas){
    // 使用Promise
    return new Promise(function(resolve,reject){
        let xhr=new XMLHttpRequest();
        let str="?";
        if($parmas){
            for(let key in $parmas){
                str+=`${key}=${$parmas[key]}&`;
            }
        };
        if($method.toUpperCase()==="GET"){
            xhr.open($method,$url+str.slice(0,-1));
            xhr.send();
        }else{
            xhr.open($method,$url);
            xhr.setRequestHeader("content-type","application/json");
            xhr.send(JSON.stringify($parmas));
        };

        xhr.addEventListener("readystatechange",function(){
            if(xhr.readyState===4){
                if(xhr.status===200){
                    // 返回成功
                    resolve(JSON.parse(xhr.response));
                }else{
                    // 返回错误
                    reject(JSON.parse(xhr.response));
                }
            }
        })
    })
}